S100A9 can induce the upregulation of PD-1/PD-L1 expression in MDSCs from S100A9 transgenic mice, and PD-1/PD-L1 blockade restores effective hematopoiesis and improves colony-forming capacity in BM mononuclear cells (MNCs) from MDS patients (Cheng et al., 2019). Here, S100A9 is linked to myelodysplastic syndrome.